Cyclic AMP, and inducers of cAMP, have been shown to influence the humoral immune response. Synthetic double-stranded polynucleotides, Poly A:U, and Poly I:C, have been shown in in vitro cellular systems to have a dose-dependent effect upon antibody formation. Low dosages of this compound stimulate antibody production; large doses inhibit the response. Using guinea pigs, we propose to determine the effect of Poly I:C on cell-mediated immunity (delayed hypersensitivity) in in vivo and in vitro systems. Dose relationships will be studied to test the effect on established delayed hypersensitivity; and in separate experiments, to determine whether induction of cell-mediated immunity can be modified or inhibited. In vivo effects will be assayed by delayed skin testing; in vitro effects will be monitored with macrophage migration as a test of the lymphokine, Migration Inhibitory Factor (MIF).